基于环形闭合涡流的激光电解自耦合协同微加工机理研究

Semiconductor materials typified by single crystalline silicon and germanium have been widely used in fields like integrated circuit (IC) chip and micro-electromechanical system (MEMS), while the processing of these materials is usually difficult due to the high hardness and brittleness, which needs to be overcome. Based on the fact that the electrical conductivity of silicon and germanium increases with an increase in temperature, a hybrid laser-electrochemical machining (HL-ECM) method is proposed, where a picosecond-pulsed laser is used to induce a transient localized conductive channel in material, and an annular vortex field is employed to introduce electrochemical machining (ECM), resulting in auto-coupling of the laser-caused thermal-mechanical effects and electrochemical anodic dissolution. In this way, minimized thermal damage, improved machining localization and better surface quality could be achieved. This project is to study the laser-caused thermal and mechanical effects on the material, prove the existence of the laser-induced localized conductive channel and analyze its dynamic evolution; in addition, the annular vortex flow field will be designed and optimized, and the laser-induced breakdown in the electrolyte and the associated energy loss will be explored; further, the methods to improve hybrid machining precision and localization will be discussed over experimental study, and the machining parameters optimization will be carried out; moreover, a comprehensive mathematical model for the HL-ECM will be developed, and simulation study is to be conducted to clarify the material removal mechanism. This project is to help reveal the interactions and synergistic effects between the laser ablation and ECM, as well as develop an efficient and precise micro-machining technology to figure out the poor machinability of the hard-brittle semiconductors.

以硅、锗为代表的半导体材料在集成电路芯片、微机电系统等领域得到了广泛应用，针对该类材料硬脆性强、传统加工工艺性差的不足，提出一种激光电解自耦合的协同微加工方法：利用硅、锗电导率随温度升高而急剧增大的特性，通过皮秒激光辐照在材料内诱导产生瞬时定域导电通道，辅以环形闭合涡流引入电解加工，无需对刀即可定域实现激光热力效应与电化学阳极溶解自动耦合协同，从而减小热损伤、提高加工定域性、改善表面质量。本项目拟研究皮秒激光热力效应，论证材料内定域导电通道存在性并分析其变化规律；设计优化环形闭合涡流流场，讨论液层内光击穿及能量损失；开展激光电解协同加工试验，探索提高加工定域性的方法，完成工艺参数优化；构建热-力-流-电多场耦合的协同加工数学模型，通过仿真研究厘清减材机理。项目研究可揭示电化学溶解与激光热力效应的交互协同作用规律，解决硬脆半导体材料常规加工工艺性差的问题，为半导体材料微制造提供一种可行方案。

本项目针对硅、锗等半导体材料硬脆性强、常规加工工艺性差的不足，提出通过皮秒激光辐照动态调控材料导电性能，诱导产生瞬时定域导电通道，并通过多种流场设计引入电解加工，定域实现激光热力效应与电化学阳极溶解自耦合协同作用，从而减小热损伤、提高加工定域性、改善表面质量。（1）根据超快激光与材料相互作用机理，构建了皮秒激光加工双温模型，并通过实验对比加以验证，对电子与晶格温度场演化、自由电子密度分布变化、相变、减材、微沟槽成形等过程开展了仿真计算，理论论证了激光对电导率定域增强作用。（2）设计搭建了低压稳定电解液射流生成系统，获得了恒速无振动电解液射流，配合设计制造的涡流生成环，初步获得了环形涡流，并对流场开展仿真建模，掌握了流速、压强分布规律。（3）构建了激光电解协同加工系统，实现了背向光控定域电解加工、激光电解同位复合加工两种不同方式；前者通过晶圆上表面激光辐照定域提高材料电导率，进而在下表面实现定域电解；后者将激光刻蚀与电解同位复合于材料同一位置。（4）开展了半导体材料背向光控电解加工试验研究，采用中性NaNO3电解液情况下，在下表面实现高效定域电解加工，深度方向减材效率可达160μm/min，证明了激光辐照可定域提高半导体材料电导率。（5）优化完善了背向光控电解加工工艺，利用电解液射流冲刷效应去除电解加工产物，得到无氧化物残留的凹坑结构；在电解液射流中引入金刚石微磨粒，利用微磨粒冲蚀效应去除产物附着，实现表面微抛光，所得表面粗糙度Sa可降至0.1μm。（6）开展了激光刻蚀与电解同位复合切槽试验研究，探索了加工参数对微槽形貌影响规律。（7）开展了不同能场单独、复合建模仿真，深入分析了射流冲击、光控定域电解等过程涉及的流场、温度场、电场演化过程。项目研究揭示了电化学溶解与激光热力效应的交互协同作用规律，可用于硬脆半导体材料高效无损减材加工，为半导体材料微制造提供了一种可行方案。